It has been common practice to reinforce natural and synthetic rubber with carbon black. There has also been work performed utilizing lignin as a reinforcement for rubber. Lignin reinforced synthetic rubber, such as SBR, does not have as good of a thermal stability as carbon black reinforced SBR. When subjected to excess milling, modulus, tensile strength reductions and an increase in elongation have resulted. Furthermore, the modulus for lignin reinforced SBR is generally low.
Synthetic rubber compositions comprising styrene, butadiene and acrylamides have been described in several U.S. patents. U.S. Pat. Nos. 3,037,963, 3,118,852 and 3,247,139 each disclose such polymer materials which are reacted with and without other monomers and with aldehydes. Resinous products and coating materials are discussed in the various patents and there is no specified utility thereof as synthetic rubber for tire construction and the like. Nor, is there any disclosure of lignin or lignin-carbon black reinforcement.
Thus, the invention set forth herein is the first instance known to me wherein a synthetic rubber such as SBR can be successfully reinforced with lignin or lignin-carbon black mixtures where the SBR has been first modified with an acrylamide.